Chromatography is a well-established and valuable technique for separating chemical and biological substances and is widely used in research and industry, finding many applications in compound preparation, purification and analysis. There are many different forms of chromatography, liquid chromatography being of particular importance in the pharmaceutical and biological industries for the preparation, purification and analysis of proteins, peptides and nucleic acids.
A typical liquid chromatography apparatus has an upright housing in which a bed of packing material, which is usually particulate in nature and consists of a porous medium, rests against a permeable retaining layer. A liquid mobile phase enters through an inlet, for example at the top of the column, usually through a porous, perforated filter, mesh or frit, moves through the bed of packing material and is removed via an outlet, typically through a second filter, mesh or frit.
In many cases it is important to obtain liquids of precisely known composition and/or other characteristics, such as pH, ionic strength, viscosity, density etc. It is further not uncommon that the composition of the liquid should not only be at each moment precisely known and controlled, but also should vary with time in a precise and controlled manner. Such liquids are usually obtained by mixing or blending two or more liquids with each other, typically using a blending system, usually an on-site blending system, which may provide for both isocratic and gradient blending modes (step gradient and linear gradient). One application where the composition of liquids is of utmost importance is in the field of liquid chromatography, when buffers having a specified pH and optionally also ionic strength are utilized, the pH and ionic strength of the eluent being the two most important parameters that control selectivity of protein separations in chromatography, such as on ion exchange resins. Another such application is filtration.
The current systems include usage of multiple high pressure pumps to deliver different solutions/buffer solution such as acid, base and salt along with water to a mixer for forming a blended solution that needs to be delivered to the chromatography column. However characteristics of the blended solution such as pH level and conductivity cannot be determined before supplying to the chromatography column. As multiple solutions need to be supplied at varying quantity and concentration, a switch valve or a quaternary valve is used. The switch valve is capable of switching between different solutions and delivering the solutions to a blending unit. A high pressure pump is generally used to pump the solutions/buffer solution from their containers through the switch valve. The characteristics of the blended solution supplied to the chromatography column are important for performing separation of proteins in an efficient manner. Determining the characteristics of the blended solution is difficult and not accurate in current systems. The switch valve in the current systems provide inaccurate blendings and not accurate at low percentages. This is because sensors for determining these characteristics may not be able to tolerate a pressure level of the solution pumped by the high pressure pump. The sensors generally can accommodate only a pressure up to 7 bar i.e. 0.7 MPa. Thus the blended solutions may not have desired characteristics or may have variation in characteristics such as pH level and conductivity. The usage of more high pressure pumps also adds to cost of the chromatography system.
Accordingly, a need exists for an improved system for inline blending of solutions for chromatography.